When there is an update available in store. If you click on the app it opens an information page where you can see the changelog for the current version of app. Some developers provide this information some doesn't. I wonder where is this information is written in app code. Is it app manifest file ?
To remind again, i don't mean in store description.
There's no built-in way to store/display a changelog. The changelog you see in some apps is handled manually, like you would do to display any other kind of information.